Permanent magnet rotating electric machine

ABSTRACT

A permanent magnet rotating electric machine includes a stator having a plurality of teeth formed in a stator core, concentrated wound armature windings wound around the plurality of teeth, and a rotor having a plurality of holes formed in a rotor core for accommodating permanent magnets. Permanent magnets are inserted into the plurality of holes of the rotor. The permanent magnets are each formed or arranged as a convex “V” and “U” with respect to the shaft of the rotor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a permanent magnetrotating electric machine having rare earth permanent magnets for afield system, which are provided in a rotor, and more particularly, to apermanent magnet rotating electric machine that is mounted in, forexample, a compressor of an air conditioner and that has concentratedwound stator windings.

[0003] 2. Description of the Related Art

[0004] Generally adopted permanent magnet rotating electric machines ofsuch a type employ permanent magnets of various shapes. For example,Domestic Republication of PCT International Publication No. WO97/31422describes a permanent magnet rotating electric machine that comprises astator, into which concentrated wound armature windings are inserted insuch a way as to surround a plurality of teeth formed in a stator core,and a rotor having permanent magnets inserted into a plurality of holes,which are formed in a rotor core and used for accommodating permanentmagnets. Improvement in efficiency of this rotating electric machine,that is, what is called output enhancement is achieved by utilizingreluctance torque.

[0005] However, although the efficiency of this permanent magnetrotating electric machine is increased by effectively utilizingreluctance torque, no consideration is given to the efficiency of asystem during driven by what is called a position sensorless inverter inthe case of 120 degree energization.

[0006] In the case of this conventional machine, consideration is givenonly to the efficiency of a motor. Especially, in a rotor structureemploying concentrated windings and utilizing reluctance torque,reluctance increases. Thus, the power factor of the rotating electricmachine decreases for that, while electric current flowing therethroughincreases. This increase in electric current results in reduction ininverter efficiency. Consequently, the system efficiency decreases, farfrom increasing.

[0007] The present invention is accomplished in view of theaforementioned problems.

[0008] Accordingly, an object of the present invention is to provide apermanent magnet rotating electric machine comprising a stator havingconcentrated windings and a rotor into which permanent magnets areembedded that can increase the system efficiency even when the rotatingelectric machine is driven by a position sensorless inverter in the caseof 120 degree energization.

SUMMARY OF THE INVENTION

[0009] When a permanent magnet rotating electric machine is driven by aposition sensorless inverter in the case of 120 degree energization, theperformance of the machine is not determined only by the efficiency ofthe rotating electric machine or motor but is finally determined by thedegree of the system efficiency defined as a product of the inverterefficiency and the efficiency of the rotating electric machine. Forexample, when the efficiency of the rotating electric machine isenhanced, an output current of the inverter increases in the case thatthe power factor of the motor decreases. Further, when the outputcurrent of the inverter increases, the voltage drop occurring in acontrol device of the inverter increases. Consequently, the inverterefficiency is reduced, so that the system efficiency is reduced, farfrom being enhanced. Thus, according to an aspect of the presentinvention, there is provided a permanent magnet rotating electricmachine comprising a stator, into which concentrated wound armaturewindings are inserted in such a way as to surround a plurality of teethformed in a stator core, and a rotor having rare earth permanent magnetsinserted into a plurality of permanent magnet holes, which are formed ina rotor core and used for accommodating permanent magnets. In thisrotating electric machine, the permanent magnets are each shaped like aconvex “V” or “U” with respect to the shaft of the rotor. Moreover, themachine is configured so that the width of the interpole core at theoutside-diameter side of the rotor is narrow, while the width of theinterpole core at the inside-diameter side of the rotor is wide.Further, a ratio of width W1, which is narrowed at the outside-diameterside of the rotor, of an interpole core between the permanent magnets towidth Xg of a gap between the stator core and the rotor core is set insuch a manner as to satisfy the following condition: 10.8≦W1/Xg≦13.2.Incidentally, the shaping of the permanent magnets like a convex “V” or“U” includes the shaping of the permanent magnets like an arc, and alsoincludes the arranging of the permanent magnets like a letter “V” or “U”by combining the permanent magnets with each other.

[0010] Consequently, the present invention provides a permanent magnetrotating electric machine that enhances system efficiency when thereluctance thereof is set at an optimum value, and the machine is drivenby a position sensorless inverter in the case of 120 degreeenergization.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other features, objects and advantages of the present inventionwill become apparent from the following description of preferredembodiments with reference to the drawings in which like referencecharacters designate like or corresponding parts throughout severalviews, and in which:

[0012]FIG. 1 is a cross sectional view of a permanent magnet rotatingelectric machine according to a first embodiment of the presentinvention;

[0013]FIG. 2 is a cross sectional view of a rotor of the firstembodiment of the present invention;

[0014]FIG. 3 is a graph illustrating the characteristics of the rotatingelectric machine according to the first embodiment of the presentinvention; and

[0015]FIG. 4 is a cross sectional view of a rotor of a second embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] First Embodiment

[0017] Hereinafter, a first embodiment of the present invention isdescribed with reference to FIGS. 1, 2, and 3.

[0018]FIG. 1 is a cross sectional view of a permanent magnet rotatingelectric machine according to a first embodiment of the presentinvention. As shown in this figure, in a permanent magnet rotatingelectric machine 1, a stator 6 is configured by winding armaturewindings 5 (consisting of concentrated U-phase windings 5A, concentratedV-phase windings 5B, and concentrated W-phase windings 5C) in aplurality of slots 4 that are formed together with teeth 3 of the statorcore 2.

[0019] A rotor 7 consists of a rotor core 8, rare earth permanentmagnets 10 respectively placed in permanent magnet inserting holes 9arranged like four convex “V”s (illustrated as corresponding to fourpoles in this embodiment) with respect of a shaft (not shown) of therotor 7, and a shaft fitting hole 11 into which the shaft (not shown) isfitted. The rotor 7 is rotatably supported through a gap formed betweenthe stator 6 and the rotor 7 so that the width Xg of the gap is thedifference between the outside diameter of the rotor 7 and the insidediameter of the stator 6.

[0020] Each of the V-shaped pattern elements is composed of the two rareearth permanent magnets 10 respectively inserted into the two permanentmagnet inserting holes 9 arranged like a letter “V”. Each of thepermanent magnet inserting holes 9 and the rare earth permanent magnets10 has a rectangular section, as viewed from a longitudinal direction ofthe shaft of the rotor 7. Each of the V-shaped pattern element is formedby arranging the two permanent magnet inserting holes 9, and thus, thetwo rare earth permanent magnets 10 to be respectively inserted to theseholes 9 so that the longitudinal axes of the two inserting holes 9 orthe two permanent magnets 10 intersect with each other at an angle atthe side of the shaft of the rotor 7.

[0021]FIG. 2 is an enlarged cross sectional view of the rotor of thefirst embodiment shown in FIG. 1. As shown in FIG. 2, rivet holes 12 forfixing the rotor core 8 are formed in the rotor 7. The width W1 of eachinterpole core 13 between adjacent ones of the V-shaped pattern elementsis such that the width thereof at the outside-diameter side of the rotor7 is relatively narrow and that the width thereof at the inside-diameterside of the rotor 7 is relatively wide.

[0022]FIG. 3 is a graph illustrating the characteristics of the rotatingelectric machine according to the first embodiment of the presentinvention. Abscissas represent W1/Xg, while ordinates represent variouskinds of efficiency or power factor (normalized by setting the maximummotor efficiency at 1.0 and setting the maximum inverter efficiency at1.0 (pu)) obtained during the rotating electric machine is driven by aposition sensorless inverter in the case of 120 degree energization.Thus, a curve connecting black circles, a curve connecting whitecircles, and a curve connecting white squares respectively represent themotor efficiency, the inverter efficiency, and the system efficiencyobtained by using the ratio (W1/Xg) as a parameter. Incidentally, “pu”values are values represented according to a per-unit method. In thiscase, the maximum value of the motor efficiency is set at 1.0 pu (thatis, what is called 100%). Similarly, the maximum value of the inverterefficiency is set at 1.0 pu. The motor efficiency and the inverterefficiency represent change in the motor efficiency and change in theinverter efficiency, which are expressed as percentages of the parameterW1/Xg. This embodiment can be applied to a motor used for driving acompressor (not shown) of an air conditioner (not shown). Usually, underconstraints due to the compressor, it is preferable that the width ofthe gap is 0.4 to 0.6 mm.

[0023] This desirable range of the width of the gap is determinedaccording to the manner of assembling the compressor. That is, the rotoris pressed into the shaft operating in cooperation with a scroll of thecompressor, while the stator is shrinkage fitted into an innercircumferential part of a compressor container. However, strictlyspeaking, the inner circumference of the stator is out of round. Thus,the position of the rotor is determined between the inner circumferenceof the stator and the outer circumference of the rotor through a spacerwith reference to the inner circumference of the stator. Therefore, thewidth of the gap may vary about 0.2 mm. Thus, to assemble the compressorby taking sufficient allowable change in width of the gap intoconsideration, preferably, the width of the gap is 0.4 to 0.6 mm.

[0024] As is seen from FIG. 3, the motor efficiency changes according tothe ratio (W1/Xg) and takes a maximum value when the ratio (W1/Xg) isclose to 12. In contrast, although the inverter efficiency changesaccording to the ratio (W1/Xg), the inverter efficiency takes a maximumvalue when the ratio (W1/Xg) is equal to or less than 10. Theperformance of the compressor depends upon the system efficiency that isthe product of the inverter efficiency and the motor efficiency. Thelower limit value of the ratio (W1/Xg) for optimizing the systemefficiency is determined by the motor efficiency, while the upper limitvalue thereof is determined by the inverter efficiency. When the valueof the ratio (W1/Xg) is in the range of 10.8 to 13.2, the systemefficiency is almost constant and takes a maximum value. Thus, theoptimum range of the value of the ratio (W1/Xg) is given by:

0.8≦W1/Xg≦13.2.

[0025] Incidentally, although the width of the interpole core 13 is setin this embodiment so that the width thereof at the inside-diameter sideof the rotor 7 is wider than the width thereof at the outside-diameterside of the rotor 7, needless to say, the width of the interpole core 13may be set so that the width thereof at the inside-diameter side of therotor 7 is equal to the width thereof at the outside-diameter sidethereof.

[0026] Second Embodiment

[0027] Next, another permanent magnet rotating electric machine, whichis a second embodiment of the present invention, is described withreference to FIG. 4. Incidentally, the description of constituentelements, which are the same as the constituent elements of the firstembodiment, is omitted herein. Further, the following descriptiondescribes only the differences between the first embodiment and thesecond embodiment.

[0028] As shown in FIG. 4, the second embodiment has rare earthpermanent magnets 10 that are shaped like a convex letter “U” or arcwith respect to the shaft of the rotor 7. Even when the U-shaped rareearth permanent magnets are provided instead of the V-shaped rare earthpermanent magnets of the first embodiment, the shape of the interpolecore portion 13 of the second embodiment is similar to that of theinterpole core portion of the first embodiment. Consequently, the secondembodiment can have effects similar to those of the first embodiment.

[0029] As is obvious from the foregoing description, according to thepresent invention, in the permanent magnet rotating electric machineemploying a stator that has concentrated windings, the rare earthpermanent magnets are each shaped like a convex “V” or “U” with respectto the shaft of the rotor. Moreover, the ratio of the width W1 of theinterpole core between the permanent magnets to the width Xg of the gapbetween the stator core and the rotor core is set in such a manner as tomeet the following condition:

0.8≦W1/Xg≦13.2.

[0030] Thus, the rotating electric machine can operate in a state inwhich the system efficiency obtained as the product of the motorefficiency and the inverter efficiency is close to a maximum valuethereof. Therefore, when the present invention is applied to acompressor, the efficiency of the compressor is enhanced. Consequently,the present invention has an advantage in that the present invention canprovide energy savings to an air conditioner using such a compressor.

[0031] As described above, the present invention provides, for instance,a permanent magnet rotating electric machine (that is, the firstmachine) having a stator, into which concentrated wound armaturewindings are inserted in such a way as to surround a plurality of teethformed in a stator core, and a rotor having rare earth permanent magnetsinserted into a plurality of permanent magnet holes, which are formed ina rotor core and used for accommodating permanent magnets. In thisrotating electric machine, the permanent magnets are each shaped like aconvex “V” or “U” with respect to the shaft of the rotor. Moreover, theratio of the width W1 of the interpole core between the permanentmagnets to the width Xg of the gap between the stator core and the rotorcore is set in such a manner as to satisfy the following condition:

0.8≦W1/Xg≦13.2.

[0032] Furthermore, an embodiment (hereunder referred to as a secondmachine) of this permanent magnet rotating electric machine isconfigured so that the width of the interpole core between the permanentmagnets at the inside-diameter side of the rotor is wider than the widthof the interpole core between the permanent magnets at theoutside-diameter side of the rotor. Moreover, the present inventionprovides a compressor configured in such a manner as to be driven by oneof the first and second machines. Furthermore, the present inventionprovides an air conditioner having the aforementioned compressor.

[0033] Thus, according to the present invention, there is provided apermanent magnet rotating electric machine that can increase the systemefficiency even when the rotating electric machine having a stator,which employs a concentrated windings, and also having apermanent-magnet-embedded type rotor is driven by a position sensorlessinverter in the case of 120 degree energization.

[0034] Although the preferred embodiments of the present invention havebeen described above, it should be understood that the present inventionis not limited thereto and that other modifications will be apparent tothose skilled in the art without departing from the sprint of theinvention.

[0035] The scope of the present invention, therefore, should bedetermined solely by the appended claims.

What is claimed is:
 1. A permanent magnet rotating electric machinecomprising: a stator having a plurality of teeth formed in a statorcore, concentrated wound armature windings wound around said pluralityof teeth; a rotor having a plurality of holes formed in a rotor core foraccommodating permanent magnets; and permanent magnets inserted intosaid plurality of holes of said rotor; wherein said permanent magnetsare each formed or arranged as a convex “V” and “U” with respect to saidshaft of said rotor.
 2. A permanent magnet rotating electric machineaccording to claim 1, wherein a width of said interpole core betweensaid permanent magnets at an inside-diameter side of said rotor is widerthan a width of said interpole core between said permanent magnets at anoutside-diameter side of said rotor.
 3. A compressor configured in sucha manner as to be driven by a permanent magnet rotating electricmachine, said permanent magnet rotating electric machine comprising: astator having a plurality of teeth formed in a stator core, concentratedwound armature windings wound around said plurality of teeth; a rotorhaving a plurality of holes formed in a rotor core for accommodatingpermanent magnets; and permanent magnets inserted into said plurality ofholes of said rotor; wherein said permanent magnets are each shaped orarranged like a convex “V” or “U” with respect to said shaft of saidrotor.
 4. An air conditioner having a compressor configured in such amanner as to be driven by a permanent magnet rotating electric machine,said permanent magnet rotating electric machine comprising: a statorhaving a plurality of teeth formed in a stator core, concentrated woundarmature windings wound around said plurality of teeth; a rotor having aplurality of holes formed in a rotor core for accommodating permanentmagnets; and permanent magnets inserted in said plurality of holes ofsaid rotor; wherein said permanent magnets are each shaped or arrangedas a convex “V” or “U” with respect to said shaft of said rotor.